Conventionally used positive electron beam resists are mainly composed of a polymer such as polymethyl methacrylate, poly(2,2,2-trifluoroethyl .alpha.-chloroacrylate) or poly(1-butenesulfone). However, these resists are disadvantageously poor in dry etching resistance. In recent years, dry etching is increasingly used in the production of photomasks, semiconductor integrated circuits, etc., and these conventional resists cannot be used satisfactorily in more cases.
On the contrary, positive photoresists mainly composed of a novolak resin and a quinonediazide compound (e.g., Japanese Patent Laid-Open (Kokai) Nos. 63-115162, 3-251845 and 4-12357) are excellent in dry etching resistance and in addition, can be developed by a non-swelling alkali aqueous solution, hence being excellent in resolution and pattern form advantageously. However, they are unpractically extremely low in sensitivity when used for electron beam lithography.
An object of the present invention is to present a positive electron beam resist composition mainly composed of a novolak resin and a quinonediazide compound, excellent in dry etching resistance and resolution and high in sensitivity.
Another object of the present invention is to present a method for forming a fine pattern specifically high in sensitivity, accurately rectangular in form and higher in resolution by using the positive electron beam resist composition.